Nano-voids in the absorber layer of thin film solar cells are suspected to be detrimental to photovoltaic performance, however, a specific assessment of their effect is complicated by their size and by the necessity to keep the sample intact and avoid border effect. Multimodal x-ray imaging is a demonstrated operando approach to correlate optoelectronic performance and chemical-physical nanoscale features of solar cells, whereas ptychographic tomography allows for their non-destructive 3D imaging.

In this contribution, we illustrate the application of these methods to a record CuInGaSe2 solar cell to quantify the effect and distribution of voids in the absorber layer. We use multimodal x-ray imaging to estimate the local impairment in the proximity of voids, and ptychographic tomography to measure the size, orientation, and shape of voids. Besides single voids, ptychographic tomography highlights the complex 3D network of material deficit structures connecting the absorber to the buffer layer and a heavier presence of voids compared to two-dimensional top-view images.

Our findings suggest that despite a local impairment of optoelectronic performance, the effect of voids at the device level has to be negligible, given the abundance of voids and the overall good photovoltaic performance of the cell. These results foster the development of adequate models to simulate structural defects and exemplify an effective synergy of synchrotron- and electron-based microscopy approaches.